Controlled Access--In controlled access, the stations consult one another to find which station has the right to send. A station cannot send unless it has been authorized by other stations.
1.Reservation--In the reservation method, a station needs to make a reservation before sending data.
Time is divided into intervals. In each interval, a reservation frame precedes the data frames sent in that interval.If there are N stations in the system, there are exactly N reservation mini slots in the
reservation frame.When a station needs to send a data frame, it makes a reservation in its own mini slot. The stations that have made reservations
can send their data frames after the reservation frame.
2.Polling--It is similar to the roll-call performed in a classroom.In Polling one device is designated as a primary station and the other devices are secondary stations.All data exchanges must be made through the primary device even when the ultimate destination is a secondary device.The primary device controls the link; the secondary devices follow its instructions.If the primary wants to receive data, it asks the secondaries if they have anything to send; this is called poll function..If there is no data, usually a “poll reject” message is sent back. If the primary wants to send data, it tells the secondary
to get ready to receive; this is called select function.
3.Token Passing--In token passing scheme, all stations are logically connected in the form of a ring and control of the access to the medium is performed using a token.A token is a special bit pattern or a small packet, usually several bits in length, which circulate from node to node. Token passing can be used with both broadcast (token bus) and sequentially connected (token ring) type of networks.
token is passed from a node to the physically adjacent node.
1.Reservation--In the reservation method, a station needs to make a reservation before sending data.
Time is divided into intervals. In each interval, a reservation frame precedes the data frames sent in that interval.If there are N stations in the system, there are exactly N reservation mini slots in the
reservation frame.When a station needs to send a data frame, it makes a reservation in its own mini slot. The stations that have made reservations
can send their data frames after the reservation frame.
2.Polling--It is similar to the roll-call performed in a classroom.In Polling one device is designated as a primary station and the other devices are secondary stations.All data exchanges must be made through the primary device even when the ultimate destination is a secondary device.The primary device controls the link; the secondary devices follow its instructions.If the primary wants to receive data, it asks the secondaries if they have anything to send; this is called poll function..If there is no data, usually a “poll reject” message is sent back. If the primary wants to send data, it tells the secondary
to get ready to receive; this is called select function.
3.Token Passing--In token passing scheme, all stations are logically connected in the form of a ring and control of the access to the medium is performed using a token.A token is a special bit pattern or a small packet, usually several bits in length, which circulate from node to node. Token passing can be used with both broadcast (token bus) and sequentially connected (token ring) type of networks.
token is passed from a node to the physically adjacent node.
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